1. Field of the Invention
The present invention is a matrix-type, controlled-release compound fertilizer exhibiting high use efficiency, and a method for preparing the same. More particularly, the present invention relates to matrix-type, controlled-release granular compound fertilizer that employs a nutrient-absorbent bulking agent to retain fertilizer ingredients over a long period of time and to release the fertilizer ingredients in a controlled manner, unlike conventional coated forms, thereby enhancing the use efficiency of fertilizer by plants, with a minimum loss, and a method for preparing the same.
2. Description of the Related Art
In the agricultural field, various fertilizers including solid granular fertilizers, liquid fertilizers, immediate-release fertilizers, and slow-releasing fertilizers have been developed and applied. Inter alia, slow-releasing fertilizers in which particles of fertilizing ingredients are coated with a polymer are predominantly used. However, coated fertilizers are likely to remain for a long period of time in soil when the coat is not degraded. In addition, since coated fertilizers are prepared using an expensive facility, such as a fluidized bed coater, a drum coater, etc., they are expensive and thus are not widely utilized. Despite these disadvantages, coated fertilizers have recently attracted keen attention as labor-saving fertilizers, which serve to mitigate the declining number of farmers, because they are slowly dissolved over a long period of time to reduce the number of required applications.
Korean Patent Application Unexamined Publication No. 19960022408A suggests a method of slowing the dissolution rate of fertilizing ingredients in which a mixture of a resin and a fertilizer is extruded through an extruder to coat the fertilizing ingredients with the resin. However, the fertilizer is problematic in terms of commercialization because the method requires the use of a large amount of the expensive resin.
Korean Patent No. 10-0850186 discloses a fertilizer composition containing poly aspartic acid as potentiator for increasing the utilization efficiency of the fertilizer provided to plants, and a method for preparing fertilizer comprising the addition of polyaspartic acid in an amount of 0.1 to 10% to compound fertilizer so as to increase the utilization efficiency of the fertilizer. The compound fertilizer prepared by this method is observed to increase in utilization efficiency because polyaspartic acid suppresses the leaching of fertilizer ingredients. However, it does not enjoy a labor-saving effect since plants need an application of supplementary fertilizer thereto.
U.S. Pat. No. 6,749,659 introduces a matrix concept to delay the dissolution of ammonium sulfate in water wherein the matrix is composed of elemental sulfur and swelling clay. The fertilizer granule is prepared by blending a fertilizer material into a liquefied mixture of sulfur and swelling clay and granulating the blend. Dissolution rates of the fertilizer granule depend on granule sizes, with the rate of release of 1 to 2 mm particles doubling that of 2 to 4 mm particles. The mechanism of controlled release of this fertilizer seems to be electrostatic interaction between negatively charged clay and ammonium ions, thereby suppressing the release of fertilizer materials.
Chinese Patent No. 101857490A discloses a compound fertilizer capable of controlling release rates of fertilizing ingredients. The controlled-release compound fertilizer is prepared by spraying a liquefied mixture of a fertilizing ingredient and a swellable humectant clay, called attapulgite, from the top of a tower-type granulator. This method, although obtaining controlled release, is complex and requires investment for a new facility
U. S. Pat. No. 7,252,697 B2 discloses a method for making controlled-release ammonium phosphate fertilizer. This method comprises mixing an ammonium phosphate slurry with a clay mineral such as zeolite, montmorillonite, etc.; acidifying the mixture with sulfuric acid; and granulating the acidified mixture. In this patent, however, there are no contents of controlled release, but only enhancement of the use efficiency of phosphate by preventing the fixation of phosphate in soil.
Leading to the present invention, intensive and thorough research into controlled-release compound fertilizer resulted in the finding that fertilizer, when prepared in a matrix-type granular form by combining a bulking agent showing high nutrient uptake with a binder to give a supplement, and evenly mixing the supplement with compound fertilizer, can be produced using a general production facility for compound fertilizer and that the matrix-type granular compound fertilizer can absorb and retain nutrients for a long period of time so that the absorbed nutrients are resistant to leaching in soil and runoff, thereby increasing the use efficiency of fertilizer by plants.